Sonoran Desert National Monument, Ariz. — This swath of desert is in full bloom. The mountainsides blanketed by towering saguaro forests are now dotted with yellow and orange Mexican poppies, purple lupine, and white chicory. The monument is home to three wilderness areas and two historic trails.

These 487,000 acres sit along a corridor between Arizona's two largest metropolitan areas, Phoenix and Tucson, where demographers predict the population will increase from 5 million people to more than 10 million by 2040.

That's a key reason, many conservation and wildlife advocates say, Congress should permanently designate this national monument and more than 800 additional federally managed properties as the National Landscape Conservation System (NLCS).

The House Natural Resources Committee moved toward that Wednesday, voting the National Landscape Conservation System Act out of committee. The bill can now be scheduled for a vote by the full House. The Senate, meanwhile, is ready to vote on a similar bill.

"Congress … took a major step toward permanently recognizing the National Landscape Conservation System," said Richard Moe, president of the National Trust for Historic Preservation, in a statement. "These places are living history books of the American West, and by unifying them into a single system under the [Bureau of Land Management's] careful management, we are ensuring that these irreplaceable treasures ... are preserved for future generations."

These disparate 860 units of land total some 26 million acres and already have some protection. In June 2000, former Interior Secretary Bruce Babbitt established the NLCS by decree to protect the "crown jewels" of the public lands managed by the BLM. The NLCS includes 15 national monuments, 13 national conservation areas, and historic trails.

But BLM officials as well as conservation and wildlife advocates say official designation of the NLCS is essential.

"While I don't have any particular reason to believe other secretaries [of the Interior] will come in and undo the system, the fact is it can be pulled apart to disparate units," says Elena Daly, BLM's director of the NLCS in Washington. "It gives us legislative authority to exist and would require legislative action to undo. It would put us on par with National Park Service."

The congressional stamp of approval also would create a systematic way to manage these areas. Currently, the 860 disparate units don't have the same designations or protections. Some were created by states, others by various departments of the federal government.

"Resource and protection issues cannot be looked at in any kind of comprehensive way until the system is authorized by Congress," says John Shepard, deputy director of The Sonoran Institute, a land conservation group.

Ms. Daly says all 860 units maintain multiple-use components; 99 percent are open for grazing, for example. Some allow for oil and mining exploration. Most permit hunting, horseback riding, hiking, and camping but without the frills of a National Park experience.

There are no hotels, concessions, or regularly scheduled ranger hikes, let alone guides and outfitters. Some are located in rugged, remote areas, and others are near communities, like the Sonoran Monument, which is only a 45-minute drive from downtown Phoenix.

"A multiple-use mandate is great, but it represents a challenge," Daly says. "Competing uses create competing management demands." Daly adds those uses and demands are going to increase as the West continues to grow at such a rapid pace. Creating a system to preserve these lands is essential, she says.

That appears evident at the Sonoran Desert National Monument. Rich Hanson, resource adviser and outdoor recreation planner for the office of the BLM here, points to areas that are being regenerated. Partly because of directing off-road vehicle traffic to designated roads and trails only and partly because of the rainy winter here, the desert is lush. Wildflowers abound, and cactuses – especially the giant saguaros and ocotillo – are plump and green. Besides some cattle grazing on this land, big-horned sheep and desert tortoises live among the rocky hills.

Then, there are the three disparate wilderness areas – each some 60,000 acres – where motorized traffic is not permitted.

Two historic trails are here. The Juan Bautista de Anza trail commemorates the 1775-76 expedition by the Spanish commander to bring colonists westward to settle San Francisco. And there's a leg of the Butterfield Stage route that ran from St. Louis to San Francisco in the mid-1800s.

"The areas and features are different, but we need to protect the objects of importance," Mr. Hanson says.